Parthia was an ancient region in northeastern Iran, situated along the southern edge of the Caspian Sea.
It was ruled by King Hirtacius in Arthur’s time, who was subject to the Emperor Lucius of Rome.
Parthia | History
The Parthian Empire emerged in the mid-third century BC following the defeat of the Seleucid Empire by the rebel leader Arsaces I. Arsaces and his successors established the Arsacid or Parthian dynasty.
Parthian military tactics were partciularly renowned for their skilled cavalry, including mounted archers. The Parthians were known for their ability to shoot arrows effectively while riding away from their enemies, a technique called the “Parthian shot.”
The Parthians often engaged in conflicts with the Roman Empire, especially in the context of the Roman-Parthian Wars. Parthia had a complex and often contentious relationship with the Roman Empire. There were numerous conflicts and diplomatic exchanges, with territories in the region often being contested. The most notable Parthian-Roman conflict was the Battle of Carrhae in 53 BC, where the Parthians, led by General Surena, defeated the Roman army led by Marcus Licinius Crassus.
Parthia was situated along the Silk Road, a network of trade routes connecting the East and West. As a result, the Parthians played a significant role in the flow of goods and cultural exchange between the Greco-Roman world and the East.
The Parthian Empire faced internal conflicts and external pressures from neighboring powers, including the rising Sassanian Empire. In the third century AD, the Sassanian king Ardashir I successfully overthrew the last Parthian ruler, Artabanus IV, marking the end of the Parthian Empire and the beginning of the Sassanian Empire.
Source
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138